The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Iraqi forces push to retake western Mosul

Iraqi forces have launched an operation to retake the western half of Mosul from the Islamic State group.

Iraqi Prime Minister Haider al-Abadi announced the start of the operation early on Sunday morning on state television, saying government forces were moving to "liberate the people of Mosul from Daesh oppression forever", using the Arabic acronym for IS.

Southwest of Mosul, near the city's IS-held airport, plumes of smoke were seen rising into the sky as coalition aircraft bombed militant positions.

Further south at an Iraqi base, federal police forces were gathering and getting ready to move north.

Iraqi forces took control of eastern Mosul last month, but the west remains in the hands of entrenched extremists.